A circuit arrangement as described in the above paragraph is known from European Patent Application EP-A-0408121 A2.
The frequency of the first drive signal in the known circuit arrangement is comparatively low, so that a lamp operated with the circuit arrangement carries a direct current which is commuted with a comparatively low frequency. The luminous efficacy of some types of discharge lamps, more in particular of some types of high-pressure discharge lamps, is comparatively high when these lamps are operated with a direct current. To prevent cataphoresis in the discharge lamp, it is often necessary to commute the direct current at a low frequency.
Disadvantages of the known circuit arrangement in the case in which the lamp operated with the circuit arrangement is a high-pressure discharge lamp are inter alia a comparatively bad take-over after lamp ignition and the lack of adequate provisions for controlling the run-up of the lamp. Take-over is here understood to mean the stabilization of the discharge in the lamp after ignition. The comparatively bad take-over of the lamp may result in the discharge initialized in the lamp by the ignition failing to stabilize, so that the lamp extinguishes. The run-up of the high-pressure discharge lamp takes place in the time interval between ignition of the high-pressure discharge lamp and the moment stationary operating conditions are achieved. The voltage across the lamp increases strongly during the run-up. As a result, the DC voltage source from which the DC-AC converter is supplied during the run-up of the lamp must supply a continually changing DC voltage, which is difficult to realize in practice.